Covert drone strikes are one of President Obama 's key national security policies . He has already authorized 283 strikes in Pakistan , six times more than the number during President George W. Bush 's eight years in office .

As a result , the number of estimated deaths from the Obama administration 's drone strikes is more than four times what it was during the Bush administration -- somewhere between 1,494 and 2,618 .

Under Obama , the drone campaign , which during the Bush administration had put emphasis on killing significant members of al Qaeda , has undergone a quiet and unheralded shift to focus increasingly on killing Taliban foot soldiers .

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To the extent that the targets of drone attacks can be ascertained , under Bush , al Qaeda members accounted for 25 % of all drone targets compared to 40 % for Taliban targets . Under Obama , only 8 % of targets were al Qaeda compared to just over 50 % for Taliban targets .

And while under Bush , about a third of all drone strikes killed a militant leader , compared to less than 13 % since President Obama took office , according to an analysis of thousands of credible media reports about the strikes undertaken by the New America Foundation .

While Bush sought to decapitate the leadership ranks of al Qaeda , Obama seems to be aiming also to collapse the entire network of allied groups , such as the Pakistani Taliban .

As a result , so-called `` signature strikes '' have become a hallmark of Obama 's drone war . These are drone attacks based on patterns of merely suspicious activity by a group of men , rather than the identification of a particular individual militant .

These have decimated the ranks of low-level combatants , killing somewhere between 1,332 to 2,326 reported militants . In April 2010 , a militant told a New York Times reporter , `` It seems they really want to kill everyone , not just the leaders . ''

Obama 's drone campaign is quite controversial : Some claim that a substantial number of civilians are killed in the attacks , while U.S. government officials assert that the civilian casualty rate is now zero .

In Pakistan , the program is deeply unpopular and the Pakistani parliament voted in April to end any authorization for the program , a vote that the United States government has simply ignored .

The New America Foundation analysis of the drone campaign in Pakistan found that :

-- The civilian casualty rate has been dropping sharply since 2008 . The number of civilians , plus `` unknowns , '' those individuals whose precise status could not be determined from media reports , reported killed by drones in Pakistan during Obama 's tenure in office were 11 % of fatalities . So far in 2012 it is close to 2 % . Under President Bush it was 33 % .

-- Conversely , the percentage of militants killed has been rising over the life of the drone program . The number of militants reported killed by drone strikes is 89 % of the fatalities under Obama compared to 67 % under Bush .

-- Some of these attacks were designed to help Pakistani interests . In the first eight months of 2009 , the U.S. carried out 19 drone strikes targeting affiliates of the leader of the Pakistani Taliban , Baitullah Mehsud , who had carried out an extensive campaign of attacks against Pakistani police officers , soldiers and politicians . Mehsud was eventually killed by a CIA drone strike .

-- Since it began in 2004 , the drone campaign has killed 49 militant leaders whose deaths have been confirmed by at least two credible news sources . While this represents a significant blow to the militant chain of command , these 49 deaths account for only 2 % of all drone-related fatalities .

Osama bin Laden himself recognized the devastation that the drones were inflicting on his organization , writing a lengthy memo about the issue in October 2010 that was later recovered in the compound in Abbottabad , Pakistan , where he was killed by a team of U.S. Navy SEALs . In the memo to a lieutenant , bin Laden advised that his men leave the Pakistani tribal regions where the drone strikes have been overwhelmingly concentrated and head to a remote part of Afghanistan and he also suggested that his son Hamza decamp for the tiny , rich Persian Gulf kingdom of Qatar .

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The year 2010 marked the most intense point of the Obama drone campaign , with a record 122 strikes . This combined with the May 2011 raid on bin Laden 's compound in Abbottabad , and the killing of at least 24 Pakistani soldiers in a NATO air strike in November severely damaged the relationship between the United States and Pakistan , and resulted in the eviction of CIA-controlled drones from Shamsi air base in Baluchistan in southwestern Pakistan .

At the same time , Cameron Munter , then-U.S. ambassador to Pakistan , was urging that there be more judicious targeting of the drone strikes as well as increased consultation with the Pakistanis about them .

In the past two years , there has also been increased congressional oversight of the program . The chairwoman of the Senate Intelligence Committee , Sen. Dianne Feinstein , D-California , explained in a May letter to the Los Angeles Times that `` Committee staff has held 28 monthly in-depth oversight meetings to review strike records and question every aspect of the program including legality , effectiveness , precision , foreign policy implications and the care taken to minimize noncombatant casualties . ''

Some combination of pushback from the State Department , increased congressional oversight , the closure of the CIA drone base in Pakistan and , perhaps , a declining number of targets in the tribal regions and a greater desire to heed Pakistani sensitivities about drone attacks has led to a sharp fall in the number of strikes since 2010 .

The number of drone strikes in 2011 fell by 40 % from the record number of strikes in 2010 . So far this year , the number of strikes has dropped by a further 25 % .

This is a welcome development . If the price of the drone campaign that increasingly kills only low-level Taliban is alienating 180 million Pakistanis -- that is too high a price to pay .

While the drone campaign in Pakistan may be on the wane , it is amping up against the al Qaeda affiliate in Yemen . This year alone , Obama has authorized around 30 drone strikes in Yemen , while Bush only launched one drone attack there during his two terms in office .

Small wonder that as Obama prepares to address the Democratic Party convention in Charlotte , North Carolina , he continues to enjoy a considerable advantage over Mitt Romney on national security .

A Reuters poll in August found Obama leading Romney by a comfortable 12 percentage points on national security , which is traditionally regarded as a Republican strength .

Thanks to Fatima Mustafa , Farhad Peikar and Jennifer Rowland for their research help .

Follow @CNNOpinion on Twitter .

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Peter Bergen : Obama 's drone campaign shifts to Taliban militants , not al Qaeda leaders

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Bergen : Obama has stepped-up drone attacks as a key part of national security policy

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Drone strikes deeply resented in Pakistan , he says , but campaign there is waning

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Yemen in the sights now , he says , as Obama ahead of Romney on national security